An access network is, for example, a coaxial cable network with a downstream (forward) channel and an upstream (return) channel which supports different bidirectional services, such as telephony, data exchange via Internet, or video telephony.
A demarcation point is described in a book entitled "Ton-und Fernsehubertragungstechnik und Technik leitungsgebundener BK-Anlagen", Decker's Verlag, G. Schenck, Heidelberg 1988, page 294. It forms the terminating unit of a public distribution network and thus provides the interface to customer premises equipment. With the demarcation point, the distribution network and an in-home network can be separated from each other for testing purposes or for blocking individual customers. The quality of the signals on the lines from the customer and on the lines from a center is measured. Customer blocking is effected manually, and the entire transmission band is blocked. During the blockage, no signal can be transmitted from the customer to the center.